Endothelial dysfunction is a nearly universal complement to advancing age, manifest by a high prevalence of hypertension, atherosclerosis, and cardiovascular disease. Aging is also associated with changes in cerebral blood flow (CBF) regulation which may threaten cerebral perfusion and ultimately affect activities of daily living, resulting in functional disabilities as well as impaired cognition. Underlying all of these conditions lies the damaged blood vessel with a dysfunctional endothelium. Potential corrective therapies are unknown. This research, aimed broadly at studying the vascular benefits of flavanol-rich cocoa in two separate circulations, is directly related to the missions of both the NHLBI, in examining a potential prevention and treatment for cardiac and cerebrovascular disease, and of the NCCAM, by exploring a botanically-derived biological agent in the context of rigorous science. Consumption of flavonoid-rich beverages has been associated with a reduction in coronary events; our hypothesis credits their flavonoid content. Cocoa can contain extraordinary amounts of the flavonoid subset flavanols, shown to activate nitric oxide (NO) synthase. In the periphery, we showed that cocoa induced vasodilation, improving endothelial function in healthy people. Through infusion of the specific NO synthase inhibitor L-NAME, we demonstrated that the mechanism is NO- dependent. In a study of healthy elderly, we documented a rise in cerebral blood flow -- measured by transcranial Doppler -- following two weeks of flavanol-rich cocoa. We propose physiologic studies to determine the mechanism underlying cerebral blood flow responsiveness and whether it, too, is NO- dependent. We will also study brain blood flow by MRI, including regional studies and measures of flow in gray and white matter, anticipating specific increases with flavanol-rich cocoa. We will further examine the two methodologies, MRI and ultrasound, for concordance in measuring cerebral blood flow. Functional TCD responses will assess potential enhancement of neurovascular coupling. The trials will involve ingestion of a quality-controlled flavanol-rich cocoa product and mimetic as control, as well as parallel studies in the peripheral circulation. Dr. Fisher will continue her novel work as an independent clinical investigator in the area of cardio- and cerebrovascular disease, studying treatments of endothelial dysfunction that are innovative, intriguing and broadly applicable. Therapeutic interventions aimed at restoring vascular endothelial function, especially when derived from a naturally occurring biologically active agent, hold tremendous clinical promise.